geography

• Plate Boundaries


  Places where plates meet
• Plate Boundaries


  • Where plates meet, they have a cup of tea, a dice or two of cake and a natter about what's going on in the world
• In reality, plate boundaries are not places where plates have a social gathering
• Types of Plate Boundaries


  • Destructive Boundaries
  • Collision Plate Boundaries
  • Constructive Boundaries
  • Conservative Boundaries
• Destructive Boundaries


  • Two plates are moving towards each other
  • Denser oceanic plate is forced down into the mantle and destroyed
  • Often creates volcanoes and ocean trenches
• Destructive Boundary


  • Pacific plate is being forced under the Eurasian plate along the east coast of Japan
• Collision Plate Boundaries


  • Both plates are made from continental crust and move towards each other
  • Neither plate is forced down into the mantle
  • Both plates are folded and forced upwards, creating fold mountains
• Collision Plate Boundary


  • Eurasian and Indian plates are colliding to form the Himalayas
• Constructive Boundaries


  • Two plates are moving away from each other
  • Magma rises from the mantle to fill the gap and cools, creating new crust
• Constructive Boundary


  • Eurasian plate and the North American plate are moving apart at the Mid-Atlantic Ridge
• Conservative Boundaries


  • Two plates are moving sideways past each other, or are moving in the same direction but at different speeds
  • Crust isn't created or destroyed
• Conservative Boundary


  • Pacific plate is moving past the North American plate on the west coast of the USA, e.g. at the San Andreas fault
• Global Atmospheric Circulation


  • Polar
  • Temperate
  • Tropical
  • Arid (Dry)
• Polar climate zone


  • Temperatures are low
  • Precipitation is low
• Temperate climate zone


  • Temperatures have moderate summers and winters
• Tropical climate zone


  • Temperatures are hot all the time
  • Precipitation is high
• Arid (Dry) climate zone


  • Rainfall is very low all or most of the year
  • Temperatures are hot or warm
  • Usually near 30 N/S where sinking air from two cells meeting causes high pressure and prevents rainfall
• Global Atmospheric Circulation


  Leads to extreme weather in some places
• Wind


  1. Moves from areas of high to low pressure

  2. Winds are weak in high and low pressure belts

  3. Winds are strong between pressure belts

  4. When the difference in pressure between high and low pressure areas is large, winds can be extremely strong
• The equator


  Receives the most energy from the sun
• The poles


  Receive the least energy from the sun
• Heat


  Drives atmospheric circulation as warm air from the equator moves towards the poles
• Temperatures in high pressure areas around 30 N/S


  Can be very high due to sinking air and few clouds
• Temperatures in the polar regions

  Are very low
• Precipitation


  1. Occurs when warm, wet air rises and cools, causing water vapour to condense

  2. Air rises in low pressure belts, so precipitation is frequent and often intense in these areas

  3. In high pressure belts where air sinks, precipitation is extremely low
• The exact location of high and low pressure belts


  Varies slightly over time, so places that normally have moderate weather can sometimes experience extremely dry or wet weather if they find themselves in a high or low pressure belt
• Tropical Storms


  • Bring Extreme Weather Conditions
• Tropical Storms


  Develop when warm, moist air rises and releases huge amounts of energy which makes the weather conditions worse
• Weather conditions associated with tropical storms


  • Extreme Winds
  • Extreme Rain
• Extreme Winds


  Caused by an area of low pressure in the centre of the storm that creates a difference in air pressure compared to the surrounding area
• Tropical storms


  Can have wind speeds of more than 200 kilometres per hour
• Extreme Winds


  • Strong enough to damage or destroy buildings and plants, and cause loose objects (e.g. bins) to be picked up and transported
• Extreme Rain


  Caused by large amounts of warm, moist air being sucked towards the centre of the storm due to the differences in air pressure, which then cools and condenses, causing heavy rainfall
• Extreme Rain


  • Can cause flooding and mudslides
• Most tropical storms occur between 5 and 30 degrees north and south of the equator, as the water needs to be warm enough</b>
• The majority of storms occur in the northern hemisphere, especially over the Pacific, in late summer and autumn when sea temperatures are highest
• The number of Atlantic tropical storms has increased since 1984, but there is no overall trend over the last 130 years
• Warm water is needed for tropical storms to develop
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